Editing Classical conditioning (section)

===Zero contingency procedure===
In this procedure, the CS is paired with the US, but the US also occurs at other times. If this occurs, it is predicted that the US is likely to happen in the absence of the CS. In other words, the CS does not "predict" the US. In this case, conditioning fails and the CS does not come to elicit a CR.<ref>{{cite journal |vauthors=Rescorla RA |title=Pavlovian conditioning and its proper control procedures |journal=Psychological Review |volume=74 |issue=1 |pages=71–80 |date=January 1967 |pmid=5341445 |doi=10.1037/h0024109 |url=http://www.uk.sagepub.com/upm-data/23600_Ch_1.pdf |access-date=2014-04-02 |archive-date=2014-04-07 |archive-url=https://web.archive.org/web/20140407062931/http://www.uk.sagepub.com/upm-data/23600_Ch_1.pdf |url-status=live }}</ref> This finding – that ''prediction'' rather than CS-US pairing is the key to conditioning – greatly influenced subsequent conditioning research and theory.